accel/tcg/translate-all: expand cpu_restore_state addr check

We are still seeing signals during translation time when we walk over
a page protection boundary. This expands the check to ensure the host
PC is inside the code generation buffer. The original suggestion was
to check versus tcg_ctx.code_gen_ptr but as we now segment the
translation buffer we have to settle for just a general check for
being inside.

I've also fixed up the declaration to make it clear it can deal with
invalid addresses. A later patch will fix up the call sites.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20171108153245.20740-2-alex.bennee@linaro.org
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Tested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

accel/tcg/translate-all.c

@@ -352,28 +352,33 @@ static int cpu_restore_state_from_tb(CPUState *cpu, TranslationBlock *tb,
     return 0;
 }
 
-bool cpu_restore_state(CPUState *cpu, uintptr_t retaddr)
+bool cpu_restore_state(CPUState *cpu, uintptr_t host_pc)
 {
     TranslationBlock *tb;
     bool r = false;
+    uintptr_t check_offset;
 
-    /* A retaddr of zero is invalid so we really shouldn't have ended
+    /* The host_pc has to be in the region of current code buffer. If
-     * up here. The target code has likely forgotten to check retaddr
+     * it is not we will not be able to resolve it here. The two cases
-     * != 0 before attempting to restore state. We return early to
+     * where host_pc will not be correct are:
-     * avoid blowing up on a recursive tb_lock(). The target must have
+     *
-     * previously survived a failed cpu_restore_state because
+     *  - fault during translation (instruction fetch)
-     * tb_find_pc(0) would have failed anyway. It still should be
+     *  - fault from helper (not using GETPC() macro)
-     * fixed though.
+     *
+     * Either way we need return early to avoid blowing up on a
+     * recursive tb_lock() as we can't resolve it here.
+     *
+     * We are using unsigned arithmetic so if host_pc <
+     * tcg_init_ctx.code_gen_buffer check_offset will wrap to way
+     * above the code_gen_buffer_size
      */
+    check_offset = host_pc - (uintptr_t) tcg_init_ctx.code_gen_buffer;
 
-    if (!retaddr) {
+    if (check_offset < tcg_init_ctx.code_gen_buffer_size) {
-        return r;
-    }
-
         tb_lock();
-    tb = tb_find_pc(retaddr);
+        tb = tb_find_pc(host_pc);
         if (tb) {
-        cpu_restore_state_from_tb(cpu, tb, retaddr);
+            cpu_restore_state_from_tb(cpu, tb, host_pc);
             if (tb->cflags & CF_NOCACHE) {
                 /* one-shot translation, invalidate it immediately */
                 tb_phys_invalidate(tb, -1);
@@ -382,6 +387,7 @@ bool cpu_restore_state(CPUState *cpu, uintptr_t retaddr)
             r = true;
         }
         tb_unlock();
+    }
 
     return r;
 }

include/exec/exec-all.h

@@ -45,6 +45,17 @@ void restore_state_to_opc(CPUArchState *env, struct TranslationBlock *tb,
                           target_ulong *data);
 
 void cpu_gen_init(void);
+
+/**
+ * cpu_restore_state:
+ * @cpu: the vCPU state is to be restore to
+ * @searched_pc: the host PC the fault occurred at
+ * @return: true if state was restored, false otherwise
+ *
+ * Attempt to restore the state for a fault occurring in translated
+ * code. If the searched_pc is not in translated code no state is
+ * restored and the function returns false.
+ */
 bool cpu_restore_state(CPUState *cpu, uintptr_t searched_pc);
 
 void QEMU_NORETURN cpu_loop_exit_noexc(CPUState *cpu);